The present invention relates to an ink dot printer comprising magnetic ink storing means provided with a magnetic ink supplying hole and an air opening; a pair of magnetic pole plates arranged opposite to each other to form a slit having one end portion immersed in magnetic ink supplied from the magnetic ink storing means; and magnetism generating means for magnetizing the paired magnetic pole plates to introduce the magnetic ink from the magnetic ink storing means to the slit so as to form a magnetic ink film in the slit. A plurality of needles are arranged adjacent to one another along the longitudinal direction of the slit, each freely movable in its longitudinal direction between a first position where one end portion is immersed in the magnetic ink film in the slit, and a second position where its one end portion projected from the magnetic ink film. Driving means selectively drives the needles to move them from the first position to the second position; wherein the single or plural needles selected force the magnetic ink, adhered on the one end portions at the first position, onto a recording paper to form dots of the magnetic ink, and wherein symbols, such as characters and numerals, are printed by the dots.
Thermal or wire dot printers are usually used as an ink dot printer. In the case of the wire dot printer, plural needles are selectively driven to directly strike a pressure-sensitive manifold paper on a platen with their end faces, or indirectly strike a recording paper with their end faces through a printing ribbon interposed between the paper and needles so as to form dots, thereby enabling symbols, such as characters and numerals, to be printed by grouping of the dots. With the conventional wire dot printer having the above-described arrangement, however, a loud noise is generated at the time of printing symbols on the pressure-sensitive manifold paper. In addition, no paper except the pressure-sensitive manifold type can be used, and the expensive printing ribbon must frequently be replaced by a new one. The expensive printing ribbon also must be used in the thermal dot printers.
In order to eliminate the drawbacks of the conventional thermal or wire dot printers, there have been proposed various kinds of ink dot printers wherein one end portion of each of plural needles is arranged in a slit formed by a pair of magnetic pole plates, the paired magnetic pole plates are magnetized to draw magnetic ink supplied from the magnetic ink storing means into the slit and adhere the magnetic ink onto the one end portions of the plural needles, and the plural needles are then selectively driven to transfer the magnetic ink on their end faces onto the recording paper on the platen so as to form dots. With the ink dot printer of this type, however, the process of supplying the liquid magnetic ink to the magnetic ink storing means is troublesome, and it often happens that the magnetic ink is caused to overflow from the magnetic ink supplying hole of the magnetic ink storing means in the course of the supplying process, or that the magnetic ink is caused to splash over the magnetic ink storing means before it reaches the magnetic ink supplying hole.
Further, that liquid magnetic ink whose viscosity has increased because it has been exposed to air in the slit for a relatively long time, when the paired magnetic pole plates are de-energized during non-use, cannot be quickly collected into the magnetic ink storing means and part of it remains in the slit due to its surface tension and dries. The dried magnetic ink thus stuck in the slit is likely to prevent the liquid magnetic ink from being drawn from the magnetic ink storing means into the slit and also prevent the operation of the needles, whose one end portions are arranged in the slit, when the ink dot printer is used again.
Furthermore, when the ink dot printer is suddenly moved or a carriage on which the paired magnetic pole plates, magnetism generating means, plural needles, driving means, and magnetic ink storing means are mounted is suddenly moved to form dots along the longitudinal center line of the platen, the magnetic ink swells in the magnetic ink storing means and sometimes jets outside through the air opening of the magnetic ink storing means.
Still furthermore, when the ink dot printer is left unused for a long time, the magnetic ink in the magnetic ink storing means dries at its surface area where it contacts air and sticks to the inner wall of the magnetic ink storing means. The dried magnetic ink thus stuck to the inner wall of the magnetic ink storing means, must be removed by detaching the magnetic ink storing means from the ink dot printer and washing it. In the case of the conventional ink dot printer, however, the longitudinal direction of the slit is substantially vertical, and the paired magnetic pole plates are inserted into and connected with the magnetic ink storing means in the longitudinal direction of the slit. Therefore, the process of releasing the connection between the paired magnetic pole plates and the magnetic ink storing means to detach the magnetic ink storing means from the ink dot printer becomes troublesome.